I think its okay for you to do whatever you want 
but I personally wouldn't do it. The decision 
(which seems to have been already made) is up to 
you, the owner of the cel. I tend to like to show 
my cels exactly how they look in real life. I 
scan any acetate (even peices that are longer 
than other peices or the image) and diplay all of 
the cel. This is just my method.

So long,
    Larg0

ps. This practice is especially visible on my 
oversized cels where many different sized peices 
of acetate may have been used to achieve a 
certain scene.